The search for new polymers and new methods of making polymers has been long and difficult. Even before this search is begun, however, the formulator must make an initial assessment of what type of polymer will optimally work to meet his or her requirements. Once those basic requirements are “identified” and a potential polymer is “envisioned” that might work to meet the basic requirements, the next task of actually making that polymer begins. In some cases the synthesis of the polymer is complicated by side reactions that occur during the synthesis process. In other cases the task is complicated by the many variables that can affect the sought after properties. For example, in many instances achieving one or more property, such as molecular weight or polydispersity, may be difficult to achieve using traditional preparation methods or conditions. Consequently, the formulator, even if he or she has a target polymer for the desired formulation, may not be able to synthesize a target polymer that has all the desired properties.
Formulators in the packaging coatings field, for example, have long sought improved coatings that can be used as a clear protective coating applied to protect the exterior paint coat of a can from smearing, marring, or degradation. One goal is to develop coating compositions that are ready for immediate use without additional preparation steps (i.e., that are “one-stage”). Preferred compositions of interest are stable in bulk quantities at standard temperature and pressure so that they may be efficiently and cost effectively shipped and stored without gellation or degradation prior to use. They also preferably are able to withstand the conditions of processing. When applied to substrates, the compositions must cure and dry rapidly (i.e., possess “snap cure” capabilities), have good adhesion to metal and other materials, be scratch resistant, and have a clear and glossy appearance.
Certain prior art coating compositions that meet these requirements are variants of formulations employed traditionally in the packaging coatings industry, including phenol/formaldehyde, urea/formaldehyde, and melamine/formaldehyde formulations. However, the widespread use of formaldehyde in production scale applications is falling into disfavor because of perceived environmental and health considerations. The unfavorable aspects of formaldehyde have spurred researchers to develop new coating formulations that contain formaldehyde scavengers. Unfortunately, such coatings have many shortcomings. For example, resins containing formaldehyde scavengers such as melamine, urea, or ammonia, frequently have low water tolerance and require the need for stabilizing emulsifiers. Rogue formaldehyde emissions, as well as additional, stability-related problems associated with heating and curing operations, also pose complications. As a result, there is a need in the packaging coatings industry for substantially formaldehyde-free hardenable compositions that are easy to use and exhibit favorable crosslinking and coating characteristics. In particular, there is a need to develop coating compositions and formulations that are stable at standard temperature and pressure so that they can be transported and stored in bulk prior to use in production scale operations. There is also a need for coating compositions and formulations that have stability and curing profiles that comport with production scale applications and are snap-curable, that adhere to substrates such as metal, that have a clear, glossy appearance, and that are mar resistant.
The above needs for the aforementioned improved coating compositions have not been met with existing commercially made polymers. The polymer compositions of the present invention may be successfully manufactured using the methods described herein and employed to solve these and other problems.